set default arguments for processFinalOperand()

with the new translator routines, processFinalOperand() will mostly be
called with only a single token pointer; the second token and operand
index arguments are only used for operators (internal functions and
parentheses tokens in old translator only); the number of operands
argument is also only used in the old translator
added new variable or defined function reference type

this is needed to distinguish between when only a variable is allowed
(INPUT and READ), or when a variable or a defined function is allowed
(a sub-string assignment) or when all including a sub-string assignment
is allowed (an assignment)

getOperand() modified to look for this new type for DefFuncN and
DefFuncP token types; getInternalFunction() modified to use the new
reference type; and added appropriate errors for new reference type in
expectedErrStatus()